Proteins alone cause prion diseases

A ROGUE, misfolded protein really is enough to trigger prion diseases such as mad cow disease, laying to rest the notion that a virus has to be involved as well.

Prion diseases seem to start with changes in the shape of the prion protein found in mammalian brains, which, mysteriously, prompt other identical prions to change shape too. These misfolded proteins build up leading to brain damage and often death, the theory goes. Since no one is sure how a rogue prion can persuade others to follow suit, some researchers have insisted a virus must also be involved.

To investigate, Walker Jackson of the Whitehead Institute in Boston, Massachusetts, and his colleagues created mice with a mutation associated with the human prion disease Fatal Familial Insomnia and injected some of their brain tissue into the brains of mice without the mutation. Crucially, both sets of mice also had a second genetic alteration, which would have made the mice resistant to FFI if the disease is triggered by a virus.

The researchers found that the first set of mice developed FFI symptoms, suggesting that the FFI mutation alone causes the prion to misfold, and the second set of mice also developed symptoms, showing that the protein change alone is enough to transmit the infection (Neuron, DOI&colon; 10.1016/j.neuron.2009.07.026).

The result should finally settle the question of whether proteins act alone to cause prion diseases, says Jackson.

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